/* * {
    margin: 0;
    padding: 0;
} */

.box {
    position: relative;
    height: 100vh;
    width: 100vw;
    border: 1px solid red;
    background-color: gray;
    /* margin: 0 auto; */
}

.yu {
    position: absolute;
    opacity: 0;
    animation: yu 2.5s cubic-bezier(0.49, -0.19, 0.83, 0.82) infinite;
    width: 100px;
    height: 100px;
    background: url("hb.jpg") no-repeat;
    background-size: 70% 100%;
}

@keyframes yu {
    0% {
        /* opacity 不透明 */
        opacity: 0;
    }
    20% {
        opacity: 1;
    }
    90% {
        opacity: 1;
    }
    100% {
        opacity: 0;
        transform: translate3d(10px, 100vh, -5px)
    }
}